Conventional base station interface architecture for RF trunking multisite switch

ABSTRACT

An interface for a conventional base station into a digitally trunked network of RF communications systems acts a pseudo-down link from a multisite switch to a trunked site controller. The interface monitors the conventional channels from the base station and sends a channel assignment message to the multisite switch when it detects a voice signal. The channel assignment message notifies the trunked RF systems that a new call is active so that each system can assign a trunked working channel to the conventional call. Similarly, the multisite switch sends a channel request when a trunked call is to be broadcast over a conventional channel. The interface keys the channel and couples the channel to the trunked call.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to the following copending commonly assignedU.S. patent applications:

Application Ser. No. 07/658,799 filed Feb. 22, 1991, which is acontinuation-in-part application to Ser. No. 07/573,977, now abandoned,entitled "Distributed Multisite Coordination System" filed on 28 Aug.1990 in the name of James L. Teel, Jr.

Application Ser. No. 07/658,843, filed Feb. 22, 1991, entitled "DynamicAddress Allocation Within RF Trunking Multisite Switch."

Application Ser. No. 07/658,640, filed Feb. 22, 1991, entitled "MessageBus Slot Update/Idle Control In RF Trunking Multisite Switch."

Application Ser. No. 07/658,637, filed Feb. 22, 1991, entitled "ProtocolBetween Console And RF Trunking System."

Application Ser. No. 07/658,641, filed Feb. 22, 1991, entitled "DataProtocol And Monitoring System For RF Trunking Multisite Switch GlobalSerial Channel."

Application Ser. No. 07/658,798, filed Feb. 22, 1991, entitled"Controller Architecture For RF Trunking Distributed Multisite Switch."

Application Ser. No. 07/658,844, filed Feb. 22, 1991, entitled"Distributed Multisite Switch Architecture."

Application Ser. No. 07/658,636, filed Feb. 22, 1991, entitled "AudioRouting With A Trunked Radio Frequency Multisite Switch."

The disclosure of each of these related copending applications isincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to radio frequency (RF) communicationssystems. More particularly, the present invention relates to aninterface that allows conventional non-trunked radio sites tocommunicate with a digitally trunked switching network for multiple site("multisite") RF communication systems.

BACKGROUND AND SUMMARY OF THE INVENTION

Trunked RF repeater systems have become a mainstay of modern RFcommunications systems used, for example, by public serviceorganizations (e.g., governmental agencies such as counties, firedepartments, police departments, etc.). RF trunked repeater systemspermit a relatively limited number of RF communications channels to beshared by a large number of users while providing relative privacy toany particular RF communication (conversation) As is well known, typicalstate-of-the-art RF repeater systems are "digitally trunked." Thesesystems use digital signals conveyed over the RF channels (inconjunction with digital control elements connected in the system) toaccomplish "trunking" (time-sharing) of the limited number of RFchannels among a large number of users.

Frequently, it is desirable for these state of the art trunked systemsto communicate with conventional non-trunked radio systems. Not allradio systems are trunked. Non-trunked conventional base stations, forexample, are still widely used. Even when a municipality puts a trunkeddigital radio system in place, it may retain some conventional basestations to reduce the cost of implementing the new system. Theseconventional base stations must be able to communicate with the users ofthe digitally trunked system to participate in the trunked system. Thepresent invention, provides an interface that allows conventional radiobase stations to communicate with a multisite switch in a digitallytrunked system.

With a conventional (non-trunked) base station, the caller manuallyselects the channel he wants to use to make a call. The caller depressesthe push-to-talk (PTT) button on his radio to broadcast the call throughthe radio system. The PTT button merely keys the microphone to theselected channel. The callees must be listening to the selected channelto hear the call. It is well-known for conventional radios to scan theavailable channels and lock-on to active channels. Many conventionalradio systems have channels dedicated to a particular group or function.For example, a police radio may have assigned channels for specificgroups of mobile units, e.g., a particular precinct, and an assignedchannel for emergency calls. In a conventional system, if a particularchannel is busy, a caller must wait for that channel to become freebefore he places a call.

In contrast to conventional base stations, digitally trunked RFcommunications systems include a "control" RF channel and several(possibly many) "working" RF channels. The working channels are used tocarry actual communications traffic (e.g., analog FM, digitized voice,digital data, etc.). The RF control channel is used to carry digitalcontrol signals between the repeater sites and user RF transceivers inthe field. When a user's transceiver is not actively engaged in aconversation, it monitors the control channel for "outbound" digitalcontrol messages directed to it. This is in contrast to scanning all orsome available channels as is done in a conventional radio system. Userdepression of the radio's push-to-talk (PTT) switch results in a digitalchannel request message requesting a working channel (and specifying oneor a group of callees) to be transmitted "inbound" over the RF controlchannel to the repeater site. The trunked repeater site (and associatedtrunking system) receives and processes the channel request message.

Assuming a working channel is available for use by the requestingcaller, the repeater site generates and transmits a responsive"outbound" channel assignment digital message over the RF controlchannel (this message has the effect of temporarily assigning theavailable working channel for use by the requesting caller's transceiverand other callee transceivers specified by the channel request message).The channel assignment message automatically directs the requestingcaller's transceiver (and callee user transceivers) to the available RFworking channel for a communications exchange.

In a trunked call, when the communications exchange terminates, thecaller's and callee's transceivers "release" the temporarily assignedworking channel and return to monitoring the RF control channel. Thereleased working channel is available for reassignment to the same ordifferent transceivers via further messages conveyed over the RF controlchannel.

To begin an audio transmission, the trunked system merely requires thecaller to wait for the next available working channel. Since theregenerally are a relatively large number of working channels, there isusually an available working channel and, if not, the wait for anavailable channel is not long. The advantage of trunking is that allworking channels are available to all callers. In a conventional radiosystem the caller waits until the channel that he has selected is free.The channel becomes free only after the prior user releases the channel.Even if all of the other channels are free, the caller on a conventionalradio must wait until his channel is free.

In contrast to the digital command messages that control the channelsand audio communications in a trunked system, a conventional basestation conveys control signals via tones or DC currents applied to theaudio signal or DC currents place on the land lines carrying audiosignals to and from the base stations. A tone controlled base stationuses a standard set of tones modulated onto the carrier frequency.Similarly, a DC current controlled base station applies a small DCcurrent to the line carrying the audio to the base station. These tonesor DC current control such base station functions as:

enable/disable repeating functions of the base station;

enable/disable the RF transmitter at the base station;

enable/disable channel guard encode/decode/monitor;

set remote, local and or/external push-to-talk, and

request Morse code identification.

Any trunked radio system that is to communicate with a conventional basestation must handle tones and DC current commands, and handlenon-trunked conventional channels. The present invention is an interfacecapable of acting as a gateway between a conventional base station and amultiple site trunked radio network.

FIG. 1 is a schematic diagram of a simplified exemplary network ofmultiple-site radio repeater system having three radio repeater(transmitting/receiving) sites S1, S2, and S3 providing communicationsto geographic areas A1, A2, and A3, respectively. Mobile or portabletransceivers within area A1 transmit signals to and receive signals fromsite S1; transceivers within area A2 transmit signals to and receivesignals transmitted by site S2; and transceivers within area A3 transmitsignals to and receive signals transmitted by site S3. For purposes ofthis illustration, two of the sites (S1 and S2) are trunked repeatersites that include a set of repeating transceivers operating on acontrol channel and plural RF working channels. The third site S3 is aconventional base station with several non-trunked channels. All threesites are connected to a central multisite switch that routes audio anddata communications between each of the sites.

Each of the two trunked sites may typically have a central sitecontroller (e.g., a digital computer) that acts as a central point forcommunications in the site, and is capable of functioning relativelyautonomously if all participants of a call are located within itsassociated coverage area. The operation of the trunked sites is verysimilar and compatible and, thus, can be relatively easily linkedtogether via a multisite switch. It is not so easy to link aconventional base station to a digitally trunked multisite switch. Theconventional base station is dissimilar to the trunked sites in that itdoes not have a control channel or equally accessible working channels.In addition, the conventional base station is tone or DC currentcontrolled, does not trunk calls, and does not use digital signaling asdo the trunked sites. Accordingly, the conventional base station is notcompatible with the trunked digital sites. Nevertheless, the multisiteswitch of the present invention is capable of establishing audiopathways between the conventional base station and the digitally trunkedradio sites.

The multisite switch is the switching network that provides control andaudio signal pathways between different trunked sites and conventionalbase stations. Such pathways must be set up at the beginning of eachcall and taken down at the end of each call because of the trunkedsystems. The multisite switch, for example, routes calls from a firstmobile radio in one site to a dispatcher console and a second mobileradio in another site. The various sites and dispatcher consoles areconnected to the multisite switch. The multisite switch is the hub of anetwork of the connected sites and dispatcher consoles. Any radio userwithin this network can talk to any other user in the network.

The multisite switch is a digital device that handles trunked digitalaudio and command signals. Such a switch is generally incompatible witha conventional non-trunked base station. The switch is set up to handledigitally trunked audio signals and the digital commands employed bytrunked RF sites. These digital commands, for example, establish calls,connect listening callees to audio pathways and disconnect calls. Aconventional radio system does not employ digital signals but ratheruses a limited set of sub-audible tones or DC currents to control itsbase station.

Unlike conventional radio systems (or a cellular radio telephone orland-based telephone environment), trunked radio system calls may berelatively short (e.g., in some cases, as short as a second or two induration). During an emergency or other period of great activity, thesystem may be required to handle hundreds of such calls in a very shorttime period. For this to occur, it is necessary to efficiently andrapidly route audio signals between the elements (i.e., RFtransmitter/receiver decks) related to any arbitrary channel of, forexample, site S1 and the elements related to any arbitrary channel ofsite S2 (and also to the elements of any arbitrary channel of site S3)to permit user transceivers in coverage areas A1 and A2 (and A3) tocommunicate with one another.

The multisite switch provides distributed audio signal routing in alarge radio system generally having a plurality of trunked radio sites,conventional base stations and dispatcher consoles. The multisite switchhas a distributed architecture so that its logical functions are sharedby various microprocessor operated nodes distributed throughout theswitch. These nodes share the computational workload of the switch andmost nodes are assigned to a specific conventional base station, trunkedsite controller, or dispatcher console. The audio routing provided bythe multisite switch is performed by audio processors within each node.By distributing the audio routing to the nodes in the switch, there isno need to have a centralized audio mixing/routing matrix that has beenrequired in prior art trunked RF switches.

In the present invention, one of the nodes in the switch is coupled toan adaptor that is specially configured to interface a conventional basestation into the switch and, thus, into the trunked radio network. Inthe preferred embodiment, the multisite node coupled to a conventionalstation is denoted as the Conventional Multisite Interface Module(CVMIM). The CVMIM node is indirectly coupled through a ConventionalInterface Adaptor (CIA) to several audio lines carrying non-trunkedconventional channels between the base station and the multisite switch.Accordingly, the CVMIM is capable of receiving and sending conventionalcalls to and from the base station. The CVMIM itself is a standard nodewithin the switch that is identical in its hardware to the ModularInterface Nodes (MIM) coupled to trunked radio sites. However, the CVMIMhas some unique programming for the conventional base station.

Within the switch, the CVMIM connects to internal time divisionmodulated (TDM) buses and control buses. These TDM slotted buses are theaudio/data pathways within the switch, the TDM buses connect each of theswitch nodes and establish digital audio links between the various sitesand dispatcher consoles within the radio network. Within the switch,there are also control buses that carry digital control messages betweennodes within the switch. These messages are used to establish, controland tear-down audio/data pathways, and to perform overheadadministrative tasks within the switch. The CVMIM switch node is coupledto the TDM buses and the control buses and, thus, interacts with all ofthe other nodes within the switch.

The CVMIM node operates within the multisite switch in conjunction witha Conventional Interface Adaptor (CIA). The CIA is a component of themultisite switch and is directly coupled to the conventional channellines between the base station and the CVMIM. The CIA does not directlyconnect to the TDM or command buses within the switch. However, the CIAhas its own internal command bus and serial command link and audio linesconnecting it to the CVMIM. The CIA converts the digitally trunkedsignals from the CVMIM to the conventional audio signals for a basestation and vice-versa. Similarly, the CIA acts on or translates thedigital control messages from the CVMIM into control tones or DCcurrents for the base station. The CIA also detects voice signals onconventional channels from the base station. The CIA makes theconventional base station appear to be a relatively standard trunkedsite to the CVMIM. The CIA forms a pseudo-downlink to the CVMIM.

The architecture of the CVMIM node includes a single controller module(preferably with a backup redundant controller module to ensurefunctionality in case of failure) supporting a plurality of audiomodules. The controller modules and audio modules may take the form ofprinted circuit boards connected to a common backplane. The audiomodules each process audio for several (e.g., four) bidirectional audiochannels. Thus, one controller board supports many (e.g., sixteen)audio/data channels. The architecture of the node and its operation arespecifically designed to enable a single controller board to handle alarge number of audio boards and channels.

The architecture of the CIA in the present invention also includes asingle controller module supported by a plurality of intelligent audioboards. The controller module is the Conventional Capabilities Interfacemodule (CCI) and is connected via a local GSC message bus to the audioboards which are each known as a Conventional Interface (CI). The CCI isalso coupled to the controller card of the CVMIM via a pseudo-downlinkconnection that is configured such that the CVMIM sees the CCI largelyas site controller for a trunked site controller. The CCI has the samehardware as does the controller in a CVMIM. Each CI audio board in theCIA has an audio line for each channel link that connects to its sisteraudio board in the CVMIM. The CI audio boards convert the trunked audiosignals to conventional audio signals and visa-versa.

Accordingly, it is an object of the present invention to allow aconventional base station to interface with a multisite network ofdigitally trunked radio system. It is a further object to provide aspecialized node in a multisite switch that is capable of communicatingwith a conventional base station.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome better and more completely understood by referring to thefollowing detailed description of presently preferred exemplaryembodiments in conjunction with the sheets of FIGURES, of which:

FIG. 1 is a schematic illustration of an exemplary multisite RFcommunications system;

FIG. 2 is a schematic of an exemplary architecture for a distributeddigitally trunked radio frequency communications system multisiteswitching network ("switch");

FIG. 3 is a block diagram of an exemplary architecture for a node of themultisite switch shown in FIG. 2;

FIG. 4 is a block diagram of an exemplary controller for the multisiteswitch node shown in FIG. 3;

FIG. 5 is a detailed block diagram of a single exemplary node of aConventional Interface Adaptor (CIA) and a Conventional MultisiteInterface Module (CVIM);

FIG. 6 is a detailed block diagram of the control architecture of theConventional Interface (CI) board of the CIA shown in the FIG. 5;

FIG. 7 is a detailed schematic diagram of an exemplary circuit forprocessing a single channel through the CI of the CIA shown in FIG. 5;

FIGS. 8 to 29 are detailed software flow charts showing the processingoperations of the Conventional Capabilities Interface (CCI) shown inFIG. 5; and

FIGS. 30 to 45 are detail software flowcharts showing the processingoperations CI controller shown in FIG. 6.

FIG. 46 illustrates some of the tones used to control conventional basestations.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

An exemplary radio repeater system 100 in accordance with the inventionis generally depicted in FIG. 1. Individual remote radio frequency (RF)transceiving units (e.g., mobile or portable radio transceivers)communicate with each other through shared radio repeaters that are partof the repeater system 100. The exemplary system 100 includes severaltrunked RF transceiver (repeater) sites 102, one or more conventionalbase stations 104, and one or more dispatch consoles 106. Each trunkedsite 102 includes plural RF transceivers (repeaters) that transmit andreceive signals over a certain area via full duplex RF channels. Forexample, site S1 transceivers over area Al. Remote RF transceivers inthe field (e.g., mobile or portable RF units) can communicate with unitswithin their own area (and also, via multisite switch 200 and othersites 102, with units in other areas). The remote units also cancommunicate with the dispatcher consoles 106 and vice versa.

Each trunked site 102 is controlled by a site controller. The sitecontroller is typically a centralized digital computer (although it maybe a distributed processor) that controls the radio frequency data andaudio traffic handled by the site. Each site controller alsocommunicates with the multisite switch 200. The multisite switch 200routes communications between sites, conventional base stations anddispatch consoles. The switch allows a talker in one RF repeater sitecoverage area (e.g. A1 shown in FIG. 1) to communicate with a talker(listener) in another area (e.g. A2) and/or with a dispatcher manningdispatch console 202. In order to increase efficiency and traffichandling capabilities (channel utilization), the exemplary preferredmultisite system preferably transmits signals only into those areaswhere the intended talkers/listeners are located. Moreover, in theexemplary multisite network environment, each trunked site independentlyassigns a specific channel to a call in coordination with channelassignments made by other sites. Similarly, the conventional basestation operates on its set of assigned frequencies. Thus, a single callmay involve repeater transceivers of several sites 102 (such repeatertransceivers generally operating on different frequencies to avoidinterference).

In the preferred multisite system 100, for example, the trunked sitecontroller (S1) receives a call from a mobile radio in coverage area A1requesting a channel to communicate with a specific callee or group ofcallees. The caller requests the channel simply by pressing thepush-to-talk (PTT) button on the microphone of his remote RFtransceiver. This informs the site controller (e.g., via an "inbound"digital control message transmitted over the RF control channel) that achannel is needed. The site controller assigns a working channel to thecall and instructs the caller's radio unit to switch from the controlchannel to the assigned working channel. This assigned working channelis thus ready to support communications within the area covered by thesite.

In addition, the site controller sends a message indicating the channelassignment to the multisite network switch 200. The switch 200, in turn,sends a channel request to all other trunked site controllers. Theswitch also routes the call to the appropriate conventional channel forthe call by keying the appropriate conventional channel. The multisiteswitch takes care of routing audio signals such that an audio signalpathway is created between the RF repeater servicing the caller and theRF repeater(s) servicing the callee(s) (additional audio signal pathwaysmay also be provided such that one or more dispatch consoles 106 maybecome involved in the communication).

Upon receiving a channel request, these "secondary" trunked sitecontrollers (they are "secondary" in the sense that they did notoriginate the call) may each assign an RF working channel to the call(e.g., if a callee designated by the caller's channel request messagehappens to be physically located within the coverage area serviced bythe associated RF transceiving site). Similarly, a user on aconventional channel can talk back by broadcasting audio on his channelthat is detected by the CIA which issues a trunked channel requestwithin the switch for the conventional call. Meanwhile, the switch 200has ensured that the caller's audio has been routed from the active RFreceiver of site S1 to active transmitters of each of the other sitesparticipating in the call.

As the call progresses (and depending upon the type of call), further RFtransceiver operators involved in the call may begin and/or ceasetransmitting. Switch 200 responds to such additional transmissions bydynamically routing further audio pathways (and mixing audio wherenecessary) such that all RF transceivers involved in the call can hearthe transmissions of all other RF transceivers involved in the call.Such additional audio routing and disconnection is performed in responseto digital messages specifying "assign" or "unkey" conditions propagatedby switch 200.

When the caller ends the call (or the call is otherwise terminated), thecaller's site controller (or possibly the site controller of anothersite handling a user transmission that is part of the call) de-assignsthe assigned channel and notifies the network switch 200 that the callis over. The network switch 200 propagates an "end of call" (e.g.,"channel drop") command to all other site controllers. The end, "unkey",of a conventional call is when the CIA no longer detects a voice signalon the channel link. The "end of call" command results in release by allsites participating in the call of all working and conventional channelsassigned to the call, and also in the multisite switch breaking all ofthe audio signal routing pathways associated with the call.

I. Multisite Switch Hardware

FIG. 2 is a more detailed schematic diagram of the architecture ofmultisite switch 200 provided by the presently preferred exemplaryembodiment of this invention. The multisite switch communicates witheach site controller 102 and dispatch console 202. There are data andaudio communication lines between the multisite switch and each sitecontroller and dispatcher console.

The primary responsibility of the multisite switch is to establish andremove audio connections between sites, conventional base stations anddispatch consoles. The multisite switch comprises a local area networkof nodes. As shown in FIG. 2, the nodes are labelled corresponding towhether they interface with a site controller, dispatch console,conventional audio system or other system component. Of importance tothis invention is the Conventional Multisite Interface Module (CVMIM)207 which is a node that communicates with conventional base stations215 through a Conventional Interface Adaptor (CIA) 212. The MultisiteInterface Modules (MIMs) 203 are nodes in the switch that interface withsite controllers and Console Interface Modules (CIMs) 204 are nodes thatinterface with dispatcher consoles. Other nodes in the switch include aMonitor Module (MOM) 205, Recorder Interface Module (RIM) 206, and aSwitch Interconnect Module (SWIM) 208. The MOM 205 is the interface forthe system manager and the MOM PC (personal computer) that havesupervisory responsibility for the switch and overall radio system.

Each node in the multisite switch (and CCI) is supported by amicroprocessor controlled controller module. All of the modules for theMIMs, CIMs, CVMIM, MOM, RIM and SWIM have the same hardware and areinterchangeable. The modules are said to have different personalities toindicate that they are assigned to, for example, a site controller,conventional base station or a dispatch console (dispatch position).Each module can be easily configured to be a MIM, CIM, etc., by settinga few switches, and are truly interchangeable.

The nodes of the switch are each connected to a digital message bus 209and a digital audio (TDM) network 210. The message bus 209 is shown inFIG. 2 as a message network using a conventional GSC digital messagingprotocol as implemented by the Intel 80C152 Global Ser. Channel (GSC)microprocessor. Such a GSC microprocessor is used as the communicationscontroller in the controller module in each node. The message bus 209 isa high speed data bus that interconnects the interface processors in thecontroller of each node.

The audio bus 210 comprises 32 time division multiplexed buses in thepreferred embodiment. Each bus contains 32 slots that each carry asingle audio channel. A maximum of 1024 audio slots may be routedthrough the switch (32 buses×32 slots), although some of the slots areused for other purposes (e.g., signalling). In the preferred embodiment,240 channels of digitized audio are carried by audio TDM network 210 toeach of the switch nodes.

The architecture and common operation of the CVMIM, MIM and CIM nodesare described in detail in Ser. No. 07/658,798 entitled "ControllerArchitecture for RF Trunking Distributed Multisite Switch" and Ser. No.07/658,636, entitled "Audio Processing Architecture Within RF TrunkingDistributed Multisite Switch", both of which are incorporated byreference.

As is shown in FIG. 3, the CVMIM 203 in the preferred embodimentincludes a controller module 410, a backup controller module 412, andplural (preferably one to eight) audio modules 400. Each of audiomodules 400 in the preferred embodiment is connected to a sisterConventional Interface (CI) audio board in the Conventional InterfaceAdaptor (CIA). The Conventional Interface CI audio boards of the CIA areconnected via land lines (other linkage) to the channels of aconventional base station via an audio link. In the preferredembodiment, each CI board provides four distinct audiosource/destination pairs. For example, in the CVMIM audio module 400(A)includes audio links 402(1)-402(4) serving associated first throughfourth conventional channels via the CIA. The CVMIM audio modules 400act as source gateways ("entrance/exit ramps") which convert audiosignals incoming from the base station into digitized audio signals(PCM) and place the digitized audio signals onto the audio TDM network210. These same audio modules 400 act as audio destinations by takingselected signals from the audio TDM network 210, converting them fromdigital into analog form, and providing the resulting analog signals tothe CIA which, in turn, provides the signals to the appropriateconventional channel for transmission by the base station.

The CVMIM controller module 410 communicates with each of the four audiomodules 400 via a common HDLC link 500 and an audio control link 600.The HDLC link 500 carries 360 K-bit serial data using HDLC protocolbetween the controller 410 and the audio modules 400. This HDLC link 500is used in the preferred embodiment to, for example, carry faultindications and messages relating to RF "channel" (i.e., channelhardware) status between the audio modules 400 and the controller module200 (additional general purpose I/0 links not shown may be providedbetween the RF site and the audio modules to convey digital alarm andstatus messages if desired). Audio control link 600 permits thecontroller module 200 to set low-level parameters (e.g., leveladjustment, TDM slot assignment, etc.) within each audio module 400(e.g., without having to obtain the cooperation of a processor installedon-board each of the audio modules).

FIG. 4 shows a block diagram of an exemplary architecture for controller410 in the CVMIM. Each controller 410 includes a communicationscontroller 301, a dual-port random-access-memory (RAM) 302 and aninterface microprocessor 303. The communications controller 301 is amessage router in the preferred embodiment. It routes messages betweenthe control message bus 209 and the interface processor 303 (thedual-port RAM 302 is used to communicate between the communicationscontroller and the interface controller 303). In the present embodiment,the communications controller 301 is an Intel 80C152 GSC microprocessor.The communications controller 301 is coupled to the GSC message bus 209.This controller 301 places messages onto the bus and receives messagesfrom the bus. Messages received from the CIA over the serial port 304are translated into a format usable by the multisite switch. Thecommunications controller also translates switch messages into a formatthat the CIA understands.

The interface processor 303 performs substantially all logical functionsfor the CVMIM. In effect, the interface processor is the intelligencefor the CVMIM. Interface processor 303 in this embodiment is an Intel80C186 microprocessor. The interface microprocessor 303 assigns TDMnetwork channels to RF transceivers by controlling the audio modules 400in the node via the parallel audio control bus 600. The interfaceprocessor 303 for each CVMIM assigns slots for audio routing purposes,connects audio slots to the conventional channels to establish acommunications link, and terminates slot assignments (note that eachCVMIM is preassigned a set of TDM bus slots for outputting audio signalsonto, and these slots are not assigned and de-assigned during the courseof normal call routing). Since all CVMIMs, MIMs and CIMs perform thesefunctions, they must continually inform each other and the other nodesof their slots assignments. Accordingly, the CVMIMs, MIMs and CIMs sendmessages regarding slot assignments, slot updates and slot idles overthe message network 209 to other nodes.

The communications controller 301 for each MIM 203 initially processesall of the messages on the message network. Slot assignments areforwarded to the interface processor 303 through the dual-port RAM.Redundant slot update/slot idle messages are not forwarded to theinterface processor by the communications controller. Messages regardingslot updates or idle slots are processed by the communicationscontroller 301 by referring to a slot bit map (database) located andmaintained in the dual-port RAM storage 302. By referring to the slotbit map, the communications controller 301 determines whether the slotstatus message conveys redundant information already known to the node,or if the slot status message conveys new information about the slot.Update messages are sent periodically by CVMIM or MIMs 203 hosting callsto confirm, to the other MIMs, CIMs and CVMIM the active status of aslot. When a host CVMIM terminates a call, it sends a slot assignmentand/or idle message to the other nodes. The primary CVMIM alsoperiodically resends idle messages until the slot is reassigned toanother call. Thus, all nodes are continually informed of the status ofall slots that have been assigned at least once.

FIG. 5 is a block diagram of a CIA 450 coupled to a CVMIM node 452 inthe preferred embodiment. The CIA has a sister CI audio board 454 foreach of the audio boards 400 associated with the CVMIM. The audio boardsare connected via analog audio lines 456. In the preferred embodiment,each audio board supports four channel lines. The CI audio boards areinterconnected via a local GSC bus that carries control messages betweenthe boards and the Conventional Capabilities Interface (CCI) 458 withinthe CIA. The CCI is a controller board that is the same as thecontroller boards in the CVMIM. The CCI translates commands from theCVMIM into commands recognizable by the CI boards. The CI boards in turnpass control commands on to the base stations 460. The CCI alsotranslates messages from the CI boards into messages recognizable by theCVMIM. To the CVMIM controller, the CCI is a pseudo downlink to atrunked site controller. It is the CCI that converts the commands for adigitally trunked system into commands for a conventional base stationand visa-versa.

The CI audio boards 454 are connected to a plurality of channel linesfrom the base station(s). In the preferred embodiment, each CI canreceive four channels over either 2- or 4-wire lines 460. Thus, the CIcan support full duplex conventional radio operations. In addition tothe audio lines, each CI has four RS232 ports 462 to the base stationthat it supports. In the preferred embodiment, these ports allow aGE-Star decoder 464 to convey decoding data to and from the multisiteswitch for encrypted conventional calls using the GE-Star decodingtechnique. In other embodiments, these ports 414 can be used to carryother data between the base station and the multisite switch.

FIG. 6 shows a block diagram of the controller architecture on each CIboard. Each CI has its own controller 501 to support the audioprocessing and routing circuitry 502. A microcontroller 504 is at theheart of the CI controller. The microcontroller 504 in the preferredembodiment is an INTEL 80C152 microcontroller. This microcontroller issupported by several external memories, including an EPROM 506, a staticRAM (SRAM) 508, and an EEPROM 510. These memories hold the operatingprograms for the microcontroller, provide scratch pad memory and holdother data used by the microcontroller. The operating programs aredescribed in detail below. An internal address and message bus 512connects the microcontroller to its external memories. This bus 512 alsoconnects the microcontroller to DIP switches 514 that are used to setthe personality of the CI board and to a discrete inputs 516 and outputs518 for an I/O user configuration interface 416 to the base station. Atthe present, the I/O port is used to support E&M signalling.

The CI microcontroller 504 communicates with the CCI over the CIA'slocal GSC bus. Similarly, the CI microcontroller communicatesinformation, e.g., decode data, directly with the base station over aseries of serial links 470 that are multiplexed 472 into themicrocontroller.

The microcontroller 504 operates the tone generation circuits 520 and DCcurrent circuits 522 that provide control commands for the conventionalbase station. As previously stated, conventional base stations aregenerally either controlled by sub-audible tones added to the audiosignal or to DC currents applied to the channel lines to the basestation. At startup, the microcontroller receives informationidentifying whether the base station is controlled by tones or DCcurrents, has 2/4 wire channel links and has E&M signalling. The tone orDC current controls are combined with the audio and VOX (voice activatedrelay) signal in circuits 524. The VOX detects audio on a conventionalchannel and sends a signal (equivalent to the signal in trunked systems)to the CVMIM indicating that the channel has been keyed or unkeyed. Thecombined audio signal is routed to the CVMIM or base station via audiorouting circuits 502.

FIG. 7 is a schematic diagram of one of the audio processing circuits onthe CI audio board. The DC current generation circuit 520 is, in thepreferred embodiment, a programmable DC current source that applies aselected current to the channel line 722 to control the conventionalbase station via transistor 724 and polarity selector switch 726.Microcontroller 504 provides data (up DATA) and control commands (upCNTRL) to set the amount of current from the DC current source and toset the polarity switch so that the current is applied with theappropriate polarity to the channel line. Similarly, the tone controlcircuits 522 comprise a programmable timer 728 and a switched captwo-pass filter 730. The microcontroller 504 sets up the timer so thatthe timer provides the appropriate tone to be applied to the audiochannel to the low-pass filter which passes the tone. The timer alsoprovides clocking information to the filter for its clock reference. Aclock reference is needed by the filter for square wave to sine waveconversion. The tone is applied by a digital EE pot gain 732 set by themicrocontroller, and the tone is added to the outgoing audio signal insummer 734. The microcontroller also sets the gain (digital EE pots 736,738) on the amplifiers for incoming and outgoing audio. Thus, the gainapplied by the CI boards can be remotely controlled via themicrocontroller 504. The CI supports 2-wire 722 and 4-wire (full duplex)740 channel lines to the base station. The CI microcontroller sendscommand signals to select 2-wire or 4-wire mode.

Audio coming from the CVMIM is amplified at 744 and summed with controltone before being sent out over the appropriate conventional channelline. Audio coming from the base station is passed directly to the CVMIMwith an appropriate amount of gain. In addition, the CI detects audiowith a VOX (voice activator relay) and then signals the microcontroller504 that audio is present. The VOX is a comparator 746 that compares therectified audio 748 to the sum 754 of a VOX threshold 750 and theaverage background noise 752 on the line. If the rectified voice audioexceeds this sum, then the comparator causes an interrupt logic 756 tosignal the CI microcontroller that the channel has been keyed. A similarinterrupt occurs when the voice audio stops and, thus, the rectifiedaudio falls off. Thus, the CI microcontroller is told that the channelhas been unkeyed.

The CCI is programmed to mimic the downlink trunking card of a trunkedsite controller. The CCI generates many of the same digital messagesthat are generated by a trunked downlink trunking card and sends thesemessages via a serial link to the controller card of the CVMIM. The CCIalso communicates with the CI audio boards in the CIA via a GSC messagebus. The CI boards, for example, send messages to the CCI when an audiosignal is detected on a conventional channel. The CCI generates anappropriate digital channel request that is sent to the CVMIM.Similarly, upon receiving a digital message from the CVMIM, the CCIsends a message on the CIA message bus instructing one of the CI boardsto generate a tone or a DC voltage level for a particular channel. Inthis way, the CCI is able to translate control information between adigital multisite switch and a conventional base station.

II. Unique Messages On Multisite Message Bus For The CVMIM and CIA

The messages on the multisite message bus that are intended solely forthe CVMIM and CIA have a unique data structure. The CVMIM also handlesmany of the same messages handled by the other switch nodes. Eachconventional message has one of two message identifications, shownbelow, followed by a message sub-identification (sub-id) defining themessage itself. A description of many of the other multisite messages iscontained in S. No. 07/658,641 entitled "Data Protocol and MonitoringSystem for RF Trunking Multisite Switch Global Ser. Channel."

The CVMIM message format allows non-CVMIM nodes in the trunked multisiteswitch receiving the message, but not needing the conventional message,to filter out the message without having to switch on each individualmessage sub id.

    ______________________________________                                        Node sends:  CONV.sub.-- MSG.sub.-- TYPE (155)                                             CONV.sub.-- MSG.sub.-- RESP (156)                                # Bytes      Field Function                                                   (1)          message.sub.-- id CONV.sub.-- MSG.sub.-- TYPE                                 or CONV.sub.-- MSG.sub.-- RESP                                   (1)          msg.sub.-- sub.sub.-- id message sub id                          (1)          site initiating/receiving                                                     site                                                             (1)          node.sub.-- id initiating/receiving                                           node id                                                          ______________________________________                                    

II(a) Conventional Base Station Control

This data structure is used to control a conventional base station froma console dispatch. All messages are initiated from a console via a CIMand are responded to from the Conventional Interface (CI) board.

    ______________________________________                                        Console sends msg.sub.-- sub.sub.-- id:                                                       REMOTE.sub.-- ENABLE                                                                           (1)                                                          REMOTE.sub.-- DISABLE                                                                          (2)                                                          REPEAT.sub.-- ENABLE                                                                           (3)                                                          REPEAT.sub.-- DISABLE                                                                          (4)                                                          CG.sub.-- ENABLE (5)                                                          CG.sub.-- DISABLE                                                                              (6)                                                          CG.sub.-- MON.sub.-- LATCH                                                                     (7)                                                          CG.sub.-- MON.sub.-- PTT                                                                       (8)                                                          SCAN.sub.-- ENABLE                                                                             (9)                                                          SCAN.sub.-- DISABLE                                                                            (10)                                                         SIM.sub.-- MON.sub.-- ENABLE                                                                   (11)                                                         SIM.sub.-- MON.sub.-- DISABLE                                                                  (12)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 1                                                             (13)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 2                                                             (14)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 3                                                             (15)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 4                                                             (16)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 1                                                             (17)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 2                                                             (18)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 3                                                             (19)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 4                                                             (20)                                                         ICOMM.sub.-- TX  (22)                                          # Bytes        Field Function                                                (1)             chn channel (1-32)                                            (1)             status status                                                 The Conventional Interface (CI) responds with                                 msg.sub.-- sub.sub.-- id:                                                                     REMOTE.sub.-- ENABLE                                                                           (1)                                                          REMOTE.sub.-- DISABLE                                                                          (2)                                                          REPEAT.sub.-- ENABLE                                                                           (3)                                                          REPEAT.sub.-- DISABLE                                                                          (4)                                                          CG.sub.-- ENABLE (5)                                                          CG.sub.-- DISABLE                                                                              (6)                                                          CG.sub.-- MON.sub.-- LATCH                                                                     (7)                                                          CG.sub.-- MON.sub.-- PTT                                                                       (8)                                                          SCAN.sub.-- ENABLE                                                                             (9)                                                          SCAN.sub.-- DISABLE                                                                            (10)                                                         SIM.sub.-- MON.sub.-- ENABLE                                                                   (11)                                                         SIM.sub.-- MON.sub.-- DISABLE                                                                  (12)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 1                                                             (13)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 2                                                             (14)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 3                                                             (15)                                                         SET.sub.-- RX.sub.-- FREQ.sub.-- 4                                                             (16)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 1                                                             (17)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 2                                                             (18)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 3                                                             (19)                                                         SET.sub.-- TX.sub.-- FREQ.sub.-- 4                                                             (20)                                                         ICOMM.sub.-- TX  (22)                                         # Bytes         Field Function                                                (1)             chn channel (1-32)                                            (1)             status return status of                                                       command                                                       ______________________________________                                    

II(b) Conventional EE Pot Control

The Conventional EE Pot Control message is used to adjust thetransmit/receive gains on the Conventional Interface (CI) board. Thesegains are set by digital pots that can be adjusted by digital commandsfrom the MOM PC.

    ______________________________________                                        MOM sends msg.sub.-- sub.sub.-- id:                                                           INCREMENT.sub.-- EE.sub.-- POT                                                                  (33)                                                        DECREMENT.sub.-- EE.sub.-- POT                                                                  (34)                                                        SET.sub.-- EE.sub.-- POT                                                                        (35)                                                        WRITE.sub.-- EE.sub.-- POT                                                                      (36)                                        # Bytes         Field Function                                                (1)             chn EE Pot channel to adjust                                  (1)             tx.sub.-- rx transmit / receive Pot                           (1)             count amount to adjust pot.                                   MOM receives msg.sub.-- sub.sub.-- id:                                                        INCREMENT.sub.-- EE.sub.-- POT                                                                  (33)                                                        DECREMENT.sub.-- EE.sub.-- POT                                                                  (34)                                                        SET.sub.-- EE.sub.-- POT                                                                        (35)                                                        WRITE.sub.-- EE.sub.-- POT                                                                      (36)                                        # Bytes         Field Function                                                (1)             chn EE Pot channel adjusted                                   (1)             tx.sub.-- rx transmit / receive Pot                           (1)             count new EE Pot level                                        ______________________________________                                    

II(c) Conventional CI EE Pot Levels

This message is initiated from the CI board and is used to report the EEPot levels at startup to the MOM PC.

    ______________________________________                                        CI sends:      CI.sub.-- EE.sub.-- POT.sub.-- LEVEL (37)                      # Bytes        Field Function                                                 (1)            chn channel (1-32)                                             (1)            tx.sub.-- rx transmit / receive Pot                            (4)            ee.sub.-- levels levels for each of                                           4 channels                                                     ______________________________________                                    

II(d) Conventional Controller Interface (CCI) Configuration/Status

The following messages are used to determine the status of the CCI card.The MOM PC sends the CCI its conventional site number and the CCIreports to the MOM when it's reset.

    ______________________________________                                        MOM sends:     CCI.sub.-- CONFIG (38)                                         # Bytes        Field Function                                                 (1)            conv.sub.-- site conventional site                                            # (1-2)                                                        CCI sends:     CCI.sub.-- RESET (39)                                          # Bytes        Field Function                                                 (1)            conv.sub.-- site conventional site                                            # reset                                                        ______________________________________                                    

II(e) CI Configuration

The CI Configuration message is used by the MOM PC to configure eacheach individual CI channels for the conventional base station.

    ______________________________________                                        MOM sends:     CI.sub.-- CONFIG (40)                                          # Bytes        Field Function                                                 (1)            chn channel to configure                                       (1)            config configuration 2/4                                                      wire, tone/DC/                                                                coupled/non-coupled, E&M                                                      signaling                                                      ______________________________________                                    

II(f) Conventional Initialization Messages

The following data structure precedes all conventional initializationmessages throughout the switch. Each message has a messageidentification (id) of CONV₁₃ INIT₁₃ MSG. This message format allowsnodes in the system receiving the message, but not needing the message,to filter out the message without having to scan through each individualmessage sub id.

    ______________________________________                                        Node sends:  CONV.sub.-- INIT.sub.-- MSG (157)                                # Bytes      Field Function                                                   (1)          message.sub.-- id CONV.sub.-- MSG.sub.-- TYPE                                 or CONV.sub.-- MSG.sub.-- RESP                                   (1)          command program command                                          (1)          conv.sub.-- site receiving                                                    conventional site                                                (1)          node.sub.-- id initiating node id                                (1)          chn channel to program                                           ______________________________________                                    

II(g) Conventional DC Program Control

The Conventional DC Program Control message is used to program aConventional Interface (CI) card for a DC current controlled basestation. The message is initiated by the MOM PC and transmitted to theCI card.

    ______________________________________                                        MOM sends:      CONV.sub.-- INIT.sub.-- MSG (157)                             # Bytes         Field Function                                                (7)             dc.sub.-- level DC levels:                                                    -11mA                                                                         -6mA                                                                          -2.5mA                                                                         0mA                                                                          +2.5mA                                                                        +6mA                                                                          +11mA                                                         ______________________________________                                    

II(h) Conventional Tone Program Control

The Conventional Tone Program Control message is used to program a CIcard for a tone base station. The message is initiated by the MOM PC andtransmitted to the CI card.

    ______________________________________                                        MOM sends:     CONV.sub.-- INIT.sub.-- MSG (157)                              # Bytes        Field Function                                                 (11)           tone.sub.-- frq                                                                        Tone frequencies:                                                             1050 Hz                                                                       1150 Hz                                                                       1250 Hz                                                                       1350 Hz                                                                       1450 Hz                                                                       1650 Hz                                                                       1750 Hz                                                                       1850 Hz                                                                       1950 Hz                                                                       2050 Hz                                               ______________________________________                                    

III. CCI Algorithms

FIG. 8 is a flow chart of the main loop processing for the '186microprocessor in the CCI. The '186 microprocessor waits to receive amessage from the dual-port RAM that connects this processor to the CCImicrocontroller. Accordingly, at start up and after it has initializedits variables, the microprocessor waits in step 802 for a message in thedual-port RAM.

The dual-port RAM is arranged so that the dual-port address of a messagefor the microprocessor indicates whether the message came from the CVMIMover the serial link, the CI board over the local GSC bus or is amessage generated by the microcontroller. Similarly, the microprocessorplaces messages in the dual-port RAM depending upon whether the messageis for the CVMIM, a CI board or the microcontroller. The manner in whichthe dual-port RAM operates and in which the microcontroller loadsmessages in the dual-port RAM to and from the serial link to the CVMIMand to and from the CIA's internal message bus in the controller cardsof the preferred embodiment is more fully described in Ser. No.07/658,798, entitled "Controller Architecture For RF TrunkingDistributed Multisite Switch." This application also describes in detailthe hardware for the CCI.

In step 804, upon being told by the dual-port RAM that a message ispending, the CCI microprocessor inputs the message from dual-port RAMinto its local RAM. As is evident from FIGS. 8A through C, there is avariety of messages that the microprocessor receives. These messages canbe generated internally within the CCI, such as a dual-port RAM bufferoverflow or error count message in step 810; by the CVMIM and sent tothe CCI over the serial downlink (serial messages); and by the CI audioboards from data obtained from the conventional base station. Uponcompletion of the routines executed in response to a message, themicroprocessor removes the message from the dual-port buffer in step 808(FIG. 8D) and waits for the next message in the dual-port RAM.

If the message is that the serial message buffer is overfilled or thatthere is a error in the count used to check the serial link, then instep 810 the microprocessor calls up the CI card polling algorithmoutlined in FIG. 9.

CI card polling is a technique used by the CCI to determine the statusof the CI boards within the CIA. If a CI card responds to a poll, thenthe CCI knows the CI board is still properly executing. If no responseis received, the CCI may bring up a redundant CI board (if one exists)to replace the non-responsive board. The CCI will also report the CIboard's failure to the MOM PC.

CI card polling is controlled by the receipt of buffer overflows orerror counts received from the 80C152 communications controller. Thesemessages are received every 390 milliseconds from the controller. Thisprovides the CCI with a frequency to control its polling algorithm. Adifferent CI board is polled every 390 milliseconds. The same frequencyis used for transmitting the site ID record to the CVMIM. The side IDtimeout expires every fifth cycle of messages which occurs every 1.95seconds. After each fifth cycle, the site ID record is transmittedserially to the CVMIM. This site ID record informs the multisite switchof the site's (CCI) status. In a trunked site, the principal indicationof a missing site ID is that the site is operative in a failsoft mode(i.e., individual trunking controllers operate without an operating sitecontroller). While this failsoft has no meaning for a conventional basestation, the absence of a site ID record for the conventional basestation tells the switch to operate in a pure trunking environment. Inother words, the absence of the site ID record will indicate a site (CCIin this case) is down.

When the CCI microprocessor receives a call request for a conventionalchannel from the CVMIM in step 812, it executes a routine (FIGS. 10A &B) to request and assign the multisite call to a conventional channel inthe base station. If the request is solely for a conventional call, step1002, then the microprocessor checks whether the requested conventionalchannel is a valid channel and whether the requested channel is alreadypatched into another call. If, in step 1004, the requested channel isalready participating in a patched call, then the existing patch isdeactivated through a patch deactivation algorithm shown in FIGS. 15A &B.

FIGS. 15A and B show the the patch deactivate algorithm. Dispatchconsoles set up patch calls so that more that one unit and/or more thatone group can participate in a call. Patch calls are similar tosimulselect calls. However, in a patched call all of the unitsparticipating in the patched call can talk to each other. In asimulselect call, only the dispatcher has the ability to talk to remoteunits and the participating units may not talk to each other. The remoteunits in a simulselect call can talk to the dispatcher.

To deactivate a patch call, the microprocessor first checks whether thesystem assigned identification (SAID) for the patch call is in its SAIDlist, step 1502. A SAID is a system assigned ID and is formed by theconsole requesting the patch or simulselect. The SAID list is built bythe CCI as console dispatchers activate and deactivate patches andsimulselects. Assuming that the patch call SAID is in the SAID list,then the CCI microprocessor executes a routine to issue channel dropmessages to the CVMIM (Conv. MIM) and, where necessary, unkey messagesto the conventional base station. For each conventional channel activein the patch call, the microprocessor, in step 1504, determines whetherthere is an incoming call from the base station or a console originatedcall and, if so, calls up a routine to output a channel drop message tothe CVMIM in steps 1506 and 1508. In addition to a channel drop, in step1508, an unkey message is sent to the CI board to release the channelfrom the patch call. In step 1510, if there is an outgoing call on theconventional channel from the multisite switch to the base station, thena channel drop message is sent to the CVMIM and an unkey message is sentto the CI board in step 1512. In any event, at least a channel dropmessage is sent to the CVMIM in step 1514. Thus, the requestedconventional channel is fully released from the prior patch call.

To generate a channel drop message to the CVMIM and a channel unkeymessage to the CI board, the CCI microprocessor calls up the channeldrop routine shown in FIG. 29. If an unkey message is required, then themicroprocessor sends an unkey message on the CIA's internal GSC messagebus to the appropriate CI board which, in turn, unkeys the channel instep 2902. In addition, a channel drop message is outputted to theCVMIM. A channel primitive is the data structure for outputting channelassignments, channel drops and channel unkeys. After processing a dropmessage, the CCI's microprocessor returns to the patch deactivealgorithm to deactivate the remaining conventional channels involved inthe prior patch call.

In FIGS. 15A and B, once all conventional channels have beendeactivated, step 1516, the CCI microprocessor sends a patch inactivemessage to the CVMIM, step 1518, so that it can inform the MOM that thepatch no longer has any active conventional channels. All incoming callsfrom the conventional base stations that were participating in the patchare converted to regular conventional calls by calling the channelassignment routine and the SAID status for the patch is changed toinactive in steps 1520 and 1522. Similarly, if the conventional channelis not a patch call, i.e., not on the SAID list, step 1524, then the CCIsends a patch inactive message to the CVMIM to remove the call from thepatch list in step 1526. After the patch call is inactivated, then theCCI microprocessor sends a conventional channel assignment, FIG. 28, tothe CVMIM in step 1006. Once a channel has been assigned, the CCImicroprocessor marks the incoming call as being active in step 1008.

If the call is a group call, e.g., patch or simulselect call, in step1010, then the CCI first checks that the group is on its SAID list, step1012, and that the SAID status is active, step 1014, before processingthe group call. If the SAID status is inactive, then the CCImicroprocessor sends a channel denied message to the CVMIM by executingin step 1016 the same routine used to process a channel assignment.However, if the SAID is listed and active, then the outgoing call isactivated on the SAID list in step 1018. If a console originated thecall, then the console identifier is stored in a CCI database in step1020, and if the requested call is an emergency then it is marked as anemergency on the SAID list in step 1022. Finally, the channel assignmentroutine is executed to output a channel assignment message to the CVMIMfor each of the conventional channels involved in the group call and tosend channel key messages to the proper CI boards and channels in step1024.

In step 814, if the CVMIM sends an unkey message for a conventionalchannel to the CCI, then the CCI microprocessor receives this messagethrough the dual-port RAM and executes the unkey routine shown in FIGS.11 A, B and C. If the unkey, is for a conventional channel inconventional call and not involved in a group call, step 1102, then theCCI microprocessor determines whether the unkeyed call was outgoing onthe channel from the multisite switch to the base station, step 1104,and, if so, whether the channel is involved in a patch call. If there isno outgoing call and the channel is in a patch call, step 1106, then theconsole call is marked as being inactive for this conventional channelin step 1108. The conventional channel is now ready for another call.

If the unkeyed channel call is outgoing from the switch to the basestation and is not a patch call, then the CCI microprocessor checkswhether the conventional channel is in a simulselect call, step 1110. Ifthe call is also not simulselect, then the CCI microprocessor determineswhether the incoming call is active of the channel, step 1112. If thechannel is not active at all, then the CCI sends a channel drop message,FIG. 29, to the CVMIM and an unkey message to the appropriate CI boardhaving this conventional channel in step 1114. If the incoming call isactive, then the CCI sends an unkey message, FIG. 27, to the CVMIM andCI board in step 1116 and marks the call as being inactive in step 1118and the console incoming call as being inactive in step 1108.

Upon dropping the channel, if the CCI finds that a patch call is pendingin step 1130, then the pending patch state is set to patch active instep 1132 and the CCI microprocessor confirms that the patch call isactive in the SAID list in steps 1134 and 1136. Then a channelassignment is sent to the CVMIM for the new conventional channel and achannel key message is sent to the CI board for the conventional channelin step 1138. In addition, the patch call is marked as being an activeoutgoing call on that conventional channel in step 1140. Moreover, if aconsole originated call is active on the patch SAID, step 1142, then theCCI microprocessor sends a channel assignment to the CVMIM so that theCVMIM's audio boards will couple the console call to the CI board (theproper TDM slot) and sends a key message so that the CI boards link theCVMIM audio output to the appropriate conventional channel in step 1144.

If the conventional channel being unkeyed is involved in a simulselectcall, then the SAID list is checked for the simulselect call in step1146. If the simulselect call is in the SAID list, the microprocessorchecks whether there is an active console call listed on the SAID, step1148, and whether there is an active incoming call from the base stationon the channel, step 1150. If not, then the CCI sends a channel drop tothe CVMIM for this conventional channel and an unkey message for thebase station to the appropriate CI board in step 1152. However, if thereis an active console originated call listed in the SAID, then the CCIsends an unkey to the CI board and CVMIM in step 1154. Similarly, if thethe conventional channel is active with an incoming call, then the CCIsends an unkey message to the appropriate CI board and the CVMIM in step1156.

If the conventional call being unkeyed is involved in a simulselect callbut the simulselect is not in the SAID list, step 1146, then the channelis checked for having an active incoming call, step 1147. If there is noincoming call, then a channel drop message is sent to the CVMIM, and anunkey message is sent to the CI board, step 1158, and the outgoing andincoming calls to the conventional channel are marked as being inactive,step 1160. However, if there is an active call on the channel, step1147, then an unkey message for the channel is sent to the CVMIM, anunkey message is sent to the CI board, step 1162, and the outgoing callto the base station is marked as being inactive, step 1164.

If the unkey is of a group call, step 1120, such as for a patch orsimulselect call, then the CCI microprocessor confirms that the call islisted in the SAID list, step 1122. If the call is involved in asimulselect call, step 1124, then a routine 1126 similar to thesimulselect subroutine (FIG. 16) is executed to drop and unkey thesimulselect call from all conventional channels.

If the unkeyed group call is a patch call, then the CCI determineswhether any conventional channels are stilled keyed into the patch callin step 1166. If not, then the outgoing call to the base station ismarked as inactive on the said, step 1168; a channel drop message issent to the CVMIM and an a channel is unkey sent to the CI board, step1170. In addition, the outgoing call is marked as being inactive for allconventional channels associated with the patch call, step 1172. Ifthere is more than one conventional channel still keyed to the patch,step 1174, then a channel unkey message is sent to the CVMIM and CIboards to remove the console originated call from all conventionalchannels, step 1176, and the inbound console call is marked as beinginactive on the SAID. If there is more than one conventional channelkeyed into the patch call, step 1174, then the channel unkey routine isexecuted to output a channel unkey to the patch SAID and an unkeymessage to the appropriate CI board in step 1178. The outgoing call tothe base station is marked as inactive, but any incoming call from thebase station remains active in step 1180. In addition, a channel unkeymessage is sent to the patch SAID for all conventional calls that do nothave active incoming calls from the base station in step 1182.

When a dispatcher sets up a patch or simulselect call that requires aconventional channel, the CVMIM sends to the CCI a series of threemessages to set up the call on the conventional channel. The firstmessage 816 is a header that identifies the patch or simulselect call,provides a system identification number (SAID) and indicates the numberof groups involved in the call. The second message 818 conveys thecollection of the groups involved in the call. The third message 820activates the call so that it can go forward.

When the CCI microprocessor receives a patch-header or asimulselect-header message 816 from the CVMIM, it adds the systemassigned identification (SAID) for the call to its SAID database andclears the patch/simulselect database record. The call is logged intothe database as being in the build state because the call has not yetbeen activated. The SAID database consists of all active system assignedID's (SAIDs) along with all of the conventional channels involved withthat SAID. In addition, there is a status word pertaining to the SAIDindicating active calls, emergency calls and console originated calls.

When the CCI microprocessor receives a patch or simulselect collectionmessage 818, it executes a patch/simulselect collection routine shown inFIG. 12. In steps 1202 and 1204, the SAID database is checked to ensurethat the SAID for the call was inserted into the database in response tothe header message. In step 1206, the call is confirmed to be in thebuild state and has not been activated. If the call is already active,then there is no reason to complete the collection algorithm. Assumingthat the call is in the build state, the CCI collects the conventionalchannels to be involved in the call from the collection message in step1208. If any of these channels are already involved in a patch orsimulselect call, step 1210, then the call being built is marked asbeing inactive in the SAID database and the call does not go through. Ifthe conventional channels are available, then the call is ready to beactivated.

Upon receipt of a patch active message 820, the CCI microprocessorexecutes the patch activate subroutine shown in FIG. 13. In thissubroutine, the SAID list is searched to ensure that the call is in thelist, step 1302, marked as being in the build state, step 1304, and thatall of the conventional channels to be involved in this call are notalready involved in another patch or simulselect call, step 1306. If anyof these checks yields a negative response, then the CCI sends a patchinactive message to the CVMIM, step 1308, and the call is marked asbeing inactive in the SAID list, step 1310. If the checks of the SAIDlist yield affirmative responses, then the CCI tells the CVMIM that thepatch is active for the conventional channels, step 1312, and sets theSAID status as being active, step 1314. The conventional channelsinvolved with the patch call are marked as being active for this SAID,step 1316. However, any conventional channels already involved inanother call (non-patch or simulselect call) are marked as having apending patch call, step 1318. Once this other call is unkeyed, then thepatch call is activated on that channel. Similarly, if the CCImicroprocessor receives a simulselect activate message, 828, then thesimulselect activate subroutine shown in FIG. 14 is executed. Thissubroutine is similar to the routine that activates a patch call.

When the CVMIM sends the CCI a patch deactivate message 830, the CCImicroprocessor runs the patch deactivate algorithm shown in FIGS. 15 Aand B and previously described. Similarly, when the CCI receives asimulselect deactivate message, 832, it executes the simulselectdeactivate algorithm shown in FIG. 16. To deactivate a simulselect call,the CCI first searches the SAID database for the call, step 1602, anddetermines whether there is an active console originated call listed onthe SAID, step 1604. If there is none, then the SAID is changed so thatall of the conventional channels participating in the call are indicatedas being no longer in the call, step 1606. The CCI sends a simulselectinactive message to the CVMIM, step 1608, and marks the SAID status asinactive in the SAID, step 1610.

If there is a console originated call still in the simulselect call,then each channel is individually removed from the call in step 1612. Toremove a channel, the CCI checks whether the channel is carrying anactive console originated call, step 1614, and whether the channel hasan active incoming call from the base station, step 1616. If the channelis active, then the CVMIM is told that the channel has been unkeyed and,for an active base station call, the CI board is told to release thechannel from the call. If there are no active calls on the channel, thena channel drop message is sent to the CVMIM and an unkey message is sentto the appropriate CI board in step 1618. Finally, the channel is markedin the SAID as having been removed from the call in step 1620. When allconventional channels have been removed, step 1622, the CVMIM is toldthat the simulselect call is inactive on its node and the SAID for thecall is marked as being inactive.

When the conventional base station keys a call on a conventionalchannel, the CI board detects the audio on that channel and sends aconventional channel key message 834, to the CCI over the CIA GSCmessage bus. As shown in FIG. 17, to notify the CVMIM that aconventional channel is keyed, the CCI marks the channel as beingactive, step 1702, and checks whether the channel is already involvedwith a patch call in step 1704. Assuming that the channel is not, theCCI in step 1706 calls up the channel assignment process shown in FIG.28. If the channel is involved in a patched call, then the SAID for thepatch call is extracted from the SAID database, step 1708, and a channelassignment message is sent to the CVMIM on the SAID in step 1710. Sincethe channel is involved in a patch call, the channel is marked as havingan incoming active call on the SAID in step 1712. So that allconventional channels in the patch call can listen to the channel havingthe incoming call, a channel assignment message for the incoming call issent to to the CVMIM for each of the other conventional channelsinvolved in the patch call and a key message is sent to the CI boardsfor these other channels in step 1714. In addition, these otherconventional channels are marked in the SAID as having active outgoingcalls in step 1716.

When an active incoming call from a conventional base station unkeys,step 836, the CCI microprocessor executes the the conventional channelunkey routine shown in FIGS. 18 A and B. The unkeyed call is marked asbeing inactive in step 1802 and the unkey channel is set to false instep 1804. The unkey channel flag is an indicator stating whether tounkey the channel or drop the channel. It is initialized to the dropstate assuming there are no other active calls on the SAID.

If the unkeyed channel is involved in a patch call, step 1808, that islisted in the SAID database, step 1810, then the CCI determines whetherother conventional channels have incoming calls from the base station,step 1812, and whether there is an active console call on the patch callin step 1814. If either of these are true, then the unkey channel isreset to true and an unkey message is sent to the CVMIM in step 1816. Ifthe unkey channel is still false, step 1818, then a channel drop messageis sent to the CVMIM, step 1820, and the incoming call is deactivated onthe SAID in step 1822.

Since the unkeyed channel was involved in a patch call, then each of theconventional channels in the patch call are checked for incoming calls(true=incoming call), step 1824. If the channel does not have anincoming call (false), then a channel drop message is sent to the CVMIMand patch SAID, and an unkey message is sent to the appropriate CI boardin step 1826. The outgoing call that corresponds to the unkeyed incomingchannel is marked as being inactive in step 1828. In step 1830, if theunkeyed channel was not the only active incoming call on the SAID, thena channel unkey message is sent to the patch SAID for this channel instep 1832. However, if the unkeyed channel was the only active incomingcall on the SAID, step 1830, then a check is made for console originatedcalls, step 1834, and for incoming calls on the channel, step 1836. Ifthere are no console calls or incoming calls on the channel, then anunkey message is sent to the patch SAID and to the appropriate CI board,step 1838. In addition, the outgoing call is marked as inactive on theconventional channel, step 1840.

If the unkeyed channel is scheduled to participate in a pending patchcall, step 1842, then the channel is marked as patch active, step 1844,and the patch group is pulled from the SAID list, step 1846. If there isan incoming call active on the patch SAID, step 1848, then the CCI sendsthe CVMIM a channel assignment message for the patch and a key messageis sent to the appropriate CI board in step 1850. If there is a consolecall active on the patch, step 1852, then a channel assignment is sentto the CVMIM for the console originated patch call and a key message issent to the appropriate CI board in step 1854. In either event, theoutgoing patch call on the conventional channel is marked as beingactive on the SAID.

There is a series of conventional channel control messages that themultisite switch can sent to the CCI via the CVMIM. These messages aredescribed above and the subroutines used to execute these messages areshown in FIGS. 21 to 25. These messages have a common header recognizedby the nodes in the multisite switch and the CCI as is evident from step838. The control messages can be used to control the base station so asto enable/disable the remote and repeat functions of the base station asin step 840. Similarly, the gain on CI audio boards can be adjusted bychanging the EE pot values, step 842; the CI boards and CCI can beconfigured by the switch, steps 844 and 846; and the transmit andreceive frequencies of the CI boards can be set in steps 848 and 850.

The CCI responds to the base station control and EE pot messages. Instep 852, the CCI receives an EE pot response from the CI board. The CCIcalls up the EE pot response message routine shown in FIG. 19. If the EEpot response message is made in response to a EE pot control message,then the pot response message is passed on to the CVMIM in step 1902.However, if the EE pot response message is in response to a CI pollrequest or to a CI initialization complete message, then the CCIprograms the CI board by sending it a configuration message and thestate table in step 1904. The CI board configuration information andstate table are held in a database in the NOVRAM on the CCI board. Thisinformation is loaded into the CI boards at startup or when the CIboards are reset during polling. In addition, in step 1906 the CCI sendsthe CVMIM the transmit (Tx) and receive (Rx) frequencies and EE potlevels for the CI boards. This information is sent to the MOM and heldby the MOM PC.

Upon receiving a base station response message, step 854, the CCIexecutes the base station response routine shown in FIG. 20. The CCIfirst sends the base station response message on to the CVMIM in step2002. If the CI board message states that a new receive Rx frequency hasbeen set successfully, steps 2004 and 2006, the CCI loads the new Rxfrequency into its database in step 2008. If the receive and transmit Txfrequencies are coupled, then the CCI loads the new Tx frequency intothe data base, step 2010, and informs the CVMIM of the new Tx frequency,step 2012. A similar procedure is followed by the CCI in response to aset Tx frequency command from the CI, step 2014.

If the CCI receives a conventional program message from a CVMIM, 856,then the conventional program control routine shown in FIG. 26 isexecuted which causes the CCI to send the CI board the state table for aparticular conventional channel. Finally, the microprocessor for the CCIupon receiving internal messages from the CCI microcontroller (80C152)echoes the message back to the microcontroller. This echoing procedureallows the microcontroller to act on its own messages without using aspecial internal microcontroller messaging scheme.

IV. Flowcharts for CI Audio Board

FIG. 30 is a flowchart for the routine executed by the microprocessor oneach CI board. The microprocessor starts a watch-dog timer routine 2802that regularly monitors the successful operation of the themicroprocessor. If the microprocessor does not timely respond to thistimer, then the microprocessor is reset. Once the variables for themicroprocessor are initialized, an initialization complete message issent to the CCI in step 2804 and the main loop routine is called up.

FIG. 31 is a flowchart of the main loop processing routine. When a CImicroprocessor has a message to send to the CCI over the CIA's GSCmessage bus, step 2902, the CI first confirms that the previoustransmission on the GSC bus is complete, step 2904, and that its messageis in its buffer queue, step 2906, and then places the message on theGSC bus, step 2908.

When the CI microprocessor receives messages from the CCI, step 2908, itexecutes the subroutine for processing received messages shown in FIG.32. Base station control messages, step 3002, are processed by firstconfirming that the message corresponds to a valid conventional channel,step 3004. If the message is a transmit (Tx) frequency state message,then the CI microprocessor executes the routine shown in FIG. 36. Instep 3402, the CI sets the current state for the selected channel to thestate indicated by the message. Using a message for channel "1" as anexample, the CI microprocessor first disables the transmission (Tx)circuit on the CI board, if the messages indicate that the channel is a2-wire channel, as opposed to a 4-wire, in step 3404. Depending upon thetype of control used in the conventional base station, the CImicroprocessor sets the E&M signalling (high), step 3406; sends anappropriate DC control current, step 3408, or sends a hold tone, step3410. The E&M signalling, tones and DC currents used to control basestations are conventional and the flowcharts of routines to produce thenecessary hold tones and DC currents are shown in FIGS. 43 and 44.

If the CCI sends the CI an unkey message, step 3008, the CI executes theunkey process shown in FIG. 35. The CI first resets the state for thechannel to non-transmit, step 3502 (FIG. 37). Assuming channel 1 isbeing unkeyed and depending upon the type of control used on the basestation, the CI either sets the E&M output to low, step 3504; resets theDC current to the last non-transmit DC level, step 3506; or stops thehold tone, step 3508. In addition, if the channel was set in a 2-wireconfiguration, the transmit (Tx) circuit on the CI board channelprocessing is enabled in step 3510.

If the CCI message received by the CCI is a base station non-transmitmessage 3010, then as is shown in FIG. 38 the CCI confirms that thenon-transmit state is valid, step 3602, and then resets the currentstate, step 3604, to the non-transmit state in step 3606. Non-transmitmessages are all messages that do not require the base station to bekeyed (i.e., no signal to be sent to a transmitter). For example, remoteenable/disable, repeat enable/disable or any message requiring basestation interface activity other than transmissions. Assuming that thechannel 1 is being reset, then the DC current, step 3608, or hold tone,step 3610, is stopped depending upon the base station type. Finally, theCI informs the CCI whether the output state for the channel has beenreset successfully, step 3612, or unsuccessfully, step 3614.

If the message from the CCI is not for base station control, 3002, thenthe message is for the CI board itself. The message, 3012, can tell theCI to increment, 3014, decrement, 3016, its EE digital pots (audio gain)or set the EE pots to a certain level, 3018. The CCI microprocessorexecutes subroutines to increment (FIG. 39) or decrement (FIG. 40) theappropriate channels EE pot levels. The current EE pot level is thenreported to the CCI (FIG. 41) which in turn sends a message to the CVMIMfor storage by the MOM PC. Similarly, the CCI can request, step 3018,the CI to write an EE pot level in an EEPROM. The transmit and receivegain levels are controlled by EE pots. Until the CI board isspecifically commanded to write the gains to the EE pots, the gains willoperate at existing levels until the board is reset/power cycled. Whenreset, the stored EE pot levels are loaded into the pots. Finally, theCCI can ask the CI to send a response message stating the current valuesof the EE pots in step 3020.

To configure the CI board for each conventional channel, the CCI sends aCI configuration message for each channel to the CI in step 3022.Generally, this configuration message is sent at startup of themultisite switch. Upon receipt of the message, the CI stores theconfiguration data specifying whether the channel is 2- or 4-wire,tone/DC controlled and has E&M signalling in step 3024. The CI alsoclears the state table for the channel in step 3036. Similarly, the CIreceives at startup a conventional initialization message, step 3028,that loads into a channel state table (FIG. 45) the tone frequencies orDC current levels needed for controlling the conventional base station.

If the CI detects audio its VOX generates a key or unkeying signal forthe conventional channel, step 2910, and the keying or unkeying messageis sent to the CCI as is shown in FIG. 33. In step 3102, upon detectingaudio, the CI determines whether the VOX issued a keying or unkeyingmessage. Depending upon the channel involved, a keying or unkeyingmessage is sent by the CI board to the CCI in steps 3104 and 3106. Sothat the message on the CIA GSC message bus identifies both the properchannel and CI board, the channel number used for the bus message iscalculated (CHN NO.=(CI CARD NO. -1) 4+CHANNEL NO. (1 to 4)) to indicateboth the proper CI board and which of the four channels on the board hasbeen keyed or unkeyed in steps 3108 and 3110.

If the conventional audio signal is encrypted, then the base stationsends decoding data to the multisite switch which in turn passes thedecoding data to the callees participating in the call. The calleesrequire the data to decode the audio signal. Accordingly, in step 2912,if the CI receives decoding data over a serial link with the basestation, then the CI outputs the data (FIG. 34) to the CCI with anappropriate designation of the coded conventional channel.

As shown in FIG. 35, the timer slot subroutine is called every fivemilliseconds and is used to control the tone operation to interface withtone controlled base stations. When interfacing with a tone controlledbase station, it requires a 2175 Hz secure-it tone, steps 3502 and 3504,at +10 dB for 125 milliseconds (used to wake-up the station), followedby a function tone, step 3506, (1090 Hz to 2090 Hz) at 0 dB for 40milliseconds (actual function itself), followed by a 2175 Hz hold tone,step 3508, at -20 dB for as long as the PTT key is pressed (if no PTT,then no hold tone)(used to hold base station in PTT state). The timerslot subroutine controls the duration and amplitude of each tone andwhether or not to generate the hold tone.

The present invention has been described in connection with what areconsidered to be the most practical and preferred embodiment. However,the present invention is not to be limited to the disclosed embodiment,but on the contrary, is intended to cover various modifications andequivalent arrangements included within the spirit and scope of theappended claims.

What is claimed is:
 1. A radio frequency (RF) communications networkhaving digitally trunked RF communication systems and a conventionalnon-trunked RF communication system comprising:an audio routingarrangement for routing trunked audio signals between digital trunked RFcommunication systems, said audio routing arrangement including adistributed architecture multisite switch having a plurality of nodesoperatively coupled to an audio bus, said nodes each having a processorcontrolling the node and audio routing through the node, and aconventional interface adapter interfacing said conventional non-trunkedradio frequency (RF) system to a processor controlled conventional nodein said audio routing arrangement, said adapter linking audio signals onconventional non-trunked RF channels to trunked RF communicationsthrough said audio bus.
 2. A RF communications network as in claim 1wherein said conventional interface adapter comprises:a conventionalinterface providing a pathway between non-trunked audio signals anddigitally trunked audio signals, and a conventional control interfaceconverting digital commands from said digitally trunked RF communicationsystem into conventional control commands for said conventionalnon-trunked RF communication system.
 3. A RF communications network asin claim 2 wherein said conventional interface comprises a voiceactivated device for detecting the presence of voice audio signals on achannel of said conventional communication system, said voice activateddevice signalling conventional control interface when voice audio ispresent on a conventional non-trunked channel.
 4. A RF communicationsnetwork as in claim 2 wherein said conventional interface comprisesmeans for summing conventional control signals with audio signals goingto said conventional non-trunked RF communications system.
 5. A RFcommunications network as in claim 2 wherein said conventional controlinterface comprises:channel assignment means for signally said digitallytrunked RF systems when a voice audio signal is present on a channelfrom said conventional non-trunked RF communication system, and keyingmeans for signalling said conventional interface means to establish anaudio pathway for a particular call from said trunked RF communicationsystem to said conventional non-trunked RF communication system.
 6. A RFcommunications network as in claim 2 wherein said conventionalnon-trunked RF communications system comprises a base stationoperatively coupled to said conventional interface and said conventionalcontrol further comprises means for providing conventional control tonesor DC currents to control said base station, said tones or DC currentsbeing provided in response to digital commands from said digitallytrunked RF communications system.
 7. A method for interfacing aconventional non-trunked radio frequency (RF) communication system to anetwork of digitally trunked RF communication systems having a multisiteswitch comprising an audio bus, a plurality of nodes each having aprocessor routing audio to the trunked systems, and said audio bus and aconventional processor controlled node routing audio between said audiobus and a conventional interface adapter in said switch and operativelyconnected to the conventional non-trunked RF communication system, saidmethod comprising the following steps by the multisite switch:(a)detecting an incoming voice signal on one of a plurality of conventionalnon-trunked audio sources coupled to the conventional interface adapter;(b) broadcasting the incoming voice signal on an audio slot within theswitch; (c) issuing a digital channel request message from theconventional node to the other nodes within the switch identifying theaudio slot having the incoming voice signal, and (d) at least one of theother nodes linking a trunked audio destination to the audio slot havingthe incoming voice signal.
 8. A method for interfacing a conventionalnon-trunked radio frequency (RF) communication system to a network ofdigitally trunked RF communication systems having a multisite switchcomprising an audio bus, a plurality of processor controlled nodeslinking audio between the audio bus and the trunked systems and aconventional processor controlled node routing audio between the audiobus and a conventional interface adapter operatively connected from theswitch to the conventional non-trunked RF communication system, saidmethod comprising the following steps by the multisite switch:(a) afirst switch node broadcasting a digitally trunked audio signal on anaudio slot within the switch; (b) the first switch node issuing adigital channel request message within the switch identifying the audioslot having the audio signal; (c) in response to the channel requestmessage, the conventional node and conventional interface adapter keyinga conventional channel link to activate the channel; (d) theconventional node coupling the conventional channel link to the audioslot having the trunked audio signal and the conventional interfaceadaptor converting the trunked audio signal into a non-trunked audiosignal.